1. Technical Field
This invention relates in general to the presentation of layered or nested overlays and in particular to the utilization of layered overlays to provide an effective three-dimensional image with a two-dimensional display medium. Still more particularly, this invention relates to the provision of an overlay function which permits the simultaneous display of a large number of overlays to form a composite display.
2. Background Art
The simultaneous display of multiple overlays or viewports is known in the prior art. For example, in multi-tasking environments it is common to have two or more applications active and displayed in viewports or "windows" which may fully or partially overlap. A known technique for handling this type of display involves a so-called "toggle" presentation wherein one of two overlapping windows is alternately displayed in accordance with the state of a control variable. This technique works well for alternately viewing one of two windows but will not permit the merging or mixing of multiple overlays to form a composite display.
Similarly, a second display technique is known for viewing layered viewports or windows which involves the utilization of a pseudo-three-dimensional cursor wherein the operator may "drive" the cursor into the display to view a layer beneath the layer being displayed. While this technique permits the user to separately view a selected one of multiple overlayed windows, it will not permit the merging or mixing of multiple overlays to form a composite display.
Recently, a system has been proposed which permits the controlled display of multiple layers of display by allowing a user to select a particular layer. For example, an architectural display of a building may be presented which depicts an outer elevation of the structure. The user may then select a second display which may depict the electrical distribution system or the plumbing system associated with the building, or some additional display which is associated with the primary display. As with the previously discussed systems, this system permits the selective presentation of one of a plurality of layered presentations but does not allow a composite presentation to be displayed.